Autothermal reforming in a fuel processor utilizing non-pyrophoric shift catalyst

ABSTRACT

A method for start-up and shut down of a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst is disclosed. Also disclosed are a computer programmed to start-up or shut down a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst or a program storage medium encoded with instruction that, when executed by a computer, start-up or shut down a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst.

The present invention is a divisional application of U.S. Ser. No.10/408,001, filed Apr. 4, 2003, the complete disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a fuel processor, and, moreparticularly, to a control system for a fuel processor.

2. Description of the Related Art

Fuel cell technology is an alternative energy source for moreconventional energy sources employing the combustion of fossil fuels. Afuel cell typically produces electricity, water, and heat from a fueland oxygen. More particularly, fuel cells provide electricity fromchemical oxidation-reduction reactions and possess significantadvantages over other forms of power generation in terms of cleanlinessand efficiency. Typically, fuel cells employ hydrogen as the fuel andoxygen as the oxidizing agent. The power generation is proportional tothe consumption rate of the reactants.

A significant disadvantage which inhibits the wider use of fuel cells isthe lack of a widespread hydrogen infrastructure. Hydrogen has arelatively low volumetric energy density and is more difficult to storeand transport than the hydrocarbon fuels currently used in most powergeneration systems. One way to overcome this difficulty is the use of“fuel processors” or “reformers” to convert the hydrocarbons to ahydrogen rich gas stream which can be used as a feed for fuel cells.Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel,require conversion for use as fuel for most fuel cells. Current art usesmulti-step processes combining an initial conversion process withseveral clean-up processes. The initial process is most often steamreforming (“SR”), autothermal reforming (“ATR”), catalytic partialoxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). Theclean-up processes are usually comprised of a combination ofdesulfurization, high temperature water-gas shift, low temperaturewater-gas shift, selective CO oxidation, or selective CO methanation.Alternative processes include hydrogen selective membrane reactors andfilters.

Thus, many types of fuels can be used, some of them hybrids with fossilfuels, but the ideal fuel is hydrogen. If the fuel is, for instance,hydrogen, then the combustion is very clean and, as a practical matter,only the water is left after the dissipation and/or consumption of theheat and the consumption of the electricity. Most readily availablefuels (e.g., natural gas, propane and gasoline) and even the less commonones (e.g., methanol and ethanol) include hydrogen in their molecularstructure. Some fuel cell implementations therefore employ a “fuelprocessor” that processes a particular fuel to produce a relatively purehydrogen stream used to fuel the fuel cell.

SUMMARY OF THE INVENTION

The invention comprises a method for start-up and shut down of a fuelprocessor including an autothermal reformer employing a non-pyrophoricshift catalyst.

In a first aspect, the invention includes a method for starting up anautothermal reformer in a fuel processor, comprising: purging thereactor of the autothermal reformer with a fuel above the upperexplosive limit of a process feed stream comprising the fuel at aninitial temperature; maintaining a non-pyrophoric shift catalyst of theautothermal reformer at a temperature sufficient to prevent condensationof water therein; heating the purged autothermal reformer reactor to thelight off temperature of the non-pyrophoric shift catalyst whilecontinuing to flow the fuel therethrough; introducing air to the heatedautothermal reformer reactor to produce an air and fuel mixtureexceeding the upper explosive limit of the fuel; and heating theautothermal reformer reactor to an operating temperature.

In a second aspect, the invention includes a method for lighting off anoxidizer in a fuel processor, comprising: purging a reactor of theoxidizer with air at an initial temperature; generating an ignition heatin at least a portion of the purged oxidizer reactor; introducing a fuelto the heated region of the oxidizer reactor, the resulting mixture ofthe fuel and the air remaining below the lower explosive limit of thefuel; and heating the oxidizer reactor containing the fuel/air mixtureto an operating temperature.

In a third aspect, the invention includes a method for shutting down anautothermal reformer employing a non-pyrophoric shift catalyst in a fuelprocessor, comprising: terminating air flow to the autothermal reformerreactor; terminating water flow to the autothermal reformer reactorafter terminating the air flow; purging the autothermal reformer reactorwith a fuel; and allowing the autothermal reformer reactor to cool to ashutdown temperature.

In a fourth aspect, the invention includes a method for shutting down anoxidizer for use with an autothermal reformer employing a non-pyrophoricshift catalyst, comprising: terminating the flow of the fuel to areactor of the oxidizer; purging the oxidizer reactor with air until thetemperature within the oxidizer reactor reaches an ambient temperature;and terminating the air flow to the purged oxidizer reactor.

In still other aspects, the invention includes a computer programmed tostart-up or shut down a fuel processor including an autothermal reformeremploying a non-pyrophoric shift catalyst or a program storage mediumencoded with instruction that, when executed by a computer, start-up orshut down a fuel processor including an autothermal reformer employing anon-pyrophoric shift catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 illustrates one particular embodiment of a fuel processor powerplant assembled and operated in accordance with the present invention;

FIG. 2 details the anode tailgas oxidizer of the fuel processor in FIG.1 and its operation;

FIG. 3A and FIG. 3B conceptually illustrate a computing apparatus as maybe used in the implementation of one particular embodiment of thepresent invention; and

FIG. 4A-FIG. 4C conceptually illustrate the start-up of the fuelprocessor first shown in FIG. 1; and

FIG. 5 graphically illustrates the reforming process of the autothermalreformer of the fuel processor first shown in FIG. 1 during the runstate in the illustrated embodiment; and

FIG. 6A-FIG. 6C conceptually illustrate the shut down of the fuelprocessor first shown in FIG. 1.

While the invention is susceptible to various modifications andalternative forms, the drawings illustrate specific embodiments hereindescribed in detail by way of example. It should be understood, however,that the description herein of specific embodiments is not intended tolimit the invention to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a developmenteffort, even if complex and time-consuming, would be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present invention is generally directed to method and apparatus forcontrolling a “fuel processor,” or “reformer,” i.e., an apparatus forconverting hydrocarbon fuel into a hydrogen rich gas. The term “fuelprocessor” shall be used herein. In the embodiment illustrated herein,the method and apparatus control a compact processor for producing ahydrogen rich gas stream from a hydrocarbon fuel for use in fuel cells.However, other fuel processors may be used in alternative embodiments.Furthermore, other possible uses are contemplated for the apparatus andmethod described herein, including any use wherein a hydrogen richstream is desired. The method and apparatus may also be used inembodiments not applicable to the production of gas streams.Accordingly, while the invention is described herein as being used inconjunction with a fuel cell, the scope of the invention is not limitedto such use.

FIG. 1 conceptually illustrates a fuel cell power plant 100 including afuel processor 102, a fuel cell 104, and an automated control system106. The fuel processor 102 is, in the illustrated embodiment, aself-contained auto-thermal reforming (“ATR”) fuel processor thatconverts pipeline-quality natural gas to fuel cell grade fuel. Thus, thepower plant 100 is a natural gas power plant, although the invention maybe practiced with alternative fuels and end applications. In theillustrated embodiment, the fuel cell 104 is a conventional ProtonExchange Membrane Fuel Cell (“PEMFC”), also known as a PolymerElectrolyte Fuel Cell (“PEFC”). However, other types of fuel cells maybe used. Note also that the fuel processor 102 is not limited to usewith fuel cells, e.g., the fuel cell 104. Product gas of the reformate108 may be used as the feed for a fuel cell, as shown, or for otherapplications where a hydrogen rich feed stream is desired. Optionally,product gas may be sent on to further processing, for example, to removethe carbon dioxide, water or other components. Thus, the invention isnot limited to use in fuel cell power plants or even in power plants.

As previously mentioned, the fuel in the illustrated embodiment isnatural gas, but may be some other type of hydrocarbon. The hydrocarbonfuel may be liquid or gas at ambient conditions as long as it can bevaporized. As used herein the term “hydrocarbon” includes organiccompounds having C—H bonds which are capable of producing hydrogen froma partial oxidation or steam reforming reaction. The presence of atomsother than carbon and hydrogen in the molecular structure of thecompound is not excluded. Thus, suitable fuels for use in the method andapparatus disclosed herein include, but are not limited to hydrocarbonfuels such as natural gas, methane, ethane, propane, butane, naphtha,gasoline, and diesel fuel, and alcohols such as methanol, ethanol,propanol, and the like.

The operation of the fuel processor 102 and the fuel cell 104 areinter-related in the illustrated embodiment. The fuel processor 102provides a hydrogen-rich effluent stream, or “reformate,” as indicatedby the graphic 108, to the fuel cell 104. The reformate 108, in theillustrated embodiment, includes hydrogen and carbon dioxide and canalso include some water, unconverted hydrocarbons, carbon monoxide,impurities (e.g., hydrogen sulfide and ammonia) and inert components(e.g., nitrogen and argon, especially if air was a component of the feedstream). Note, however, that the precise composition of the reformate108 is implementation specific and not material to the practice of theinvention.

Still referring to FIG. 1, the fuel processor 102 of the illustratedembodiment comprises several modular physical subsystems, namely:

-   -   an autothermal reformer (“ATR”) 110 that performs the        oxidation-reduction reaction that reforms a fuel 112 input to        the fuel processor 102 into a reformate 105 for a fuel cell 104;    -   an oxidizer (“Ox”) 114, which is an anode tailgas oxidizer        (“ATO”) in the illustrated embodiment, that mixes water 116,        fuel 112, and air 118 to create a fuel mixture, or “process feed        stream”, 120 delivered to the ATR 110;    -   a fuel subsystem 122, that delivers an input fuel 112 (natural        gas, in the illustrated embodiment) to the oxidizer 114 for        mixing into the process feed stream 120 delivered to the ATR        110;    -   a water subsystem 124, that delivers the water 116 to the        oxidizer 114 for mixing into the process feed stream 120        delivered to the ATR 110;    -   an air subsystem 126, that delivers air 118 to the oxidizer 114        for mixing into the process feed stream 120 delivered to the ATR        110; and    -   a thermal subsystem 128, that controls temperatures in the        operation of the ATR 110 by circulating a coolant 113        therethrough.        Particular embodiments of the oxidizer 114 and the ATR 110 are        disclosed more fully below. The fuel subsystem 122, water        subsystem 124, air subsystem 125, and thermal subsystem 128 may        be implemented in any manner known to the art suitable for        achieving the operational characteristics of the oxidizer 114        and ATR 110.

FIG. 2A depicts one particular implementation of the oxidizer 114. Theoxidizer 114 receives fuel, water, and air through the feeds ATO1, ATO2,ATO3, ATO4 via the lines 202, 204, 206, 208, described above, from thefuel subsystem 122, water subsystem 124, the air subsystem 126, and theATR 110 through a plurality of check valves 210. The feed ATO3 is from awater separation system (discussed below) associated with the ATR 110.Exhaust 212 from the anode (not shown) of the fuel cell 103 is returnedto a water separator 214, that separates out the water that is drainedvia the solenoid valve 216 to the drain pan 218. The dehydrated anodereturn is then supplied to the oxidizer 114 via a check valve 210through the line 220. The fuel, air, and dehydrated anode return arethen mixed in the mixer 222, before introduction to the reactor 224 ofthe oxidizer 114. The resultant mixture is then heated by the electricheater 233.

Still referring to FIG. 2A, the oxidizer 114 also receives fuel, air,and water from the fuel subsystem 122, the water subsystem 124, and theair subsystem 126 through the feeds ATO5, ATO6, ATO2 over the lines 226,228, and 230, respectively, described above. The lines 226 and 228 areprotected by check valves 210. Air and fuel received over the lines 226,and 228 enter the enclosed coil 232. Water received over the line 230enters the enclosed coil 234. The heated air, water, and fuel mixture inthe reactor 224 heats the contents of the enclosed coils 232, 234, whichare then mixed in the mixer 236 and provided to the ATR 110 through thefeed ATR2 over the line 238. The oxidizer 114 is vented to an exhaust240 through a line 242.

FIG. 2B depicts one particular implementation of the ATR 110. The ATR110 comprises several stages 250 a- 250 e, including numerous heatexchangers 252 and electric heaters 233. Each of the heat exchangers 252receives temperature controlled coolant (not shown) from the thermalsubsystem 128 over the lines 256-258 and returns it over the lines 260.The exceptions are the heat exchangers 252 in the preferential oxidizing(“prox”) stage 262, which receives the coolant (not shown) from thethermal subsystem 128 over the line 264 and returns it to the thermalsubsystem 128 via line 260 and the feed TS1. The reformate gas exitingthe ATR 110 passes through a preferential oxidizer 262, is heated by theheat exchanger 252, dehydrated by the water separator 214, filtered, andsupplied to the anode (not shown) of the fuel cell 103 (shown in FIG.1).

Note that the shift 250 d employs a non-pyrophoric shift catalyst, notshown. Non-pyrophoric shift catalysts are those that typically do notincrease in temperature more than 200° C. when exposed to air afterinitial reduction. Non-pyrophoric shift catalysts may be based onprecious metals, e.g., platinum or non-precious metals, e.g., copper.One commercially available non-pyrophoric shift catalyst suitable foruse with the present invention is the SELECTRA SHIFT™ available from:

-   -   Engelhard Corporation 101 Wood Avenue Iselin, N.J. 08830 (732)        205-5000        However, other suitable non-pyrophoric shift catalysts may be        used.

Returning to FIG. 1, the automated control system 106 controls theoperation of the fuel processor 102, as indicated by the graphic 110. Insome embodiments, the automated control system 106 may control theoperation of the fuel cell 104 in addition to the fuel processor 102.The automated control system 106 is largely implemented in software on acomputing apparatus, such as the rack-mounted computing apparatus 300illustrated in FIG. 3A and FIG. 3B. Note that the computing apparatus300 need not be rack-mounted in all embodiments. Indeed, this aspect ofany given implementation is not material to the practice of theinvention. The computing apparatus 300 may be implemented as a desktoppersonal computer, a workstation, a notebook or laptop computer, anembedded processor, or the like.

The computing apparatus 300 illustrated in FIG. 3A and FIG. 3B includesa processor 305 communicating with storage 310 over a bus system 315.The storage 310 may include a hard disk and/or random access memory(“RAM”) and/or removable storage such as a floppy magnetic disk 317 andan optical disk 320. The storage 310 is encoded with a data structure325 storing the data set acquired as discussed above, an operatingsystem 330, user interface software 335, and an application 365. Theuser interface software 335, in conjunction with a display 340,implements a user interface 345. The user interface 345 may includeperipheral I/O devices such as a key pad or keyboard 350, a mouse 355,or a joystick 360. The processor 305 runs under the control of theoperating system 330, which may be practically any operating systemknown to the art. The application 365 is invoked by the operating system330 upon power up, reset, or both, depending on the implementation ofthe operating system 330. In the illustrated embodiment, the application365 includes the control system 100 illustrated in FIG. 1.

Thus, at least some aspects of the present invention will typically beimplemented as software on an appropriately programmed computing device,e.g., the computing apparatus 300 in FIG. 3A and FIG. 3B. Theinstructions may be encoded on, for example, the storage 310, the floppydisk 317, and/or the optical disk 320. The present invention thereforeincludes, in one aspect, a computing apparatus programmed to perform themethod of the invention. In another aspect, the invention includes aprogram storage device encoded with instructions that, when executed bya computing apparatus, perform the method of the invention.

Some portions of the detailed descriptions herein may consequently bepresented in terms of a software-implemented process involving symbolicrepresentations of operations on data bits within a memory in acomputing system or a computing device. These descriptions andrepresentations are the means used by those in the art to mosteffectively convey the substance of their work to others skilled in theart. The process and operation require physical manipulations ofphysical quantities. Usually, though not necessarily, these quantitiestake the form of electrical, magnetic, or optical signals capable ofbeing stored, transferred, combined, compared, and otherwisemanipulated. It has proven convenient at times, principally for reasonsof common usage, to refer to these signals as bits, values, elements,symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantifies. Unlessspecifically stated or otherwise as may be apparent, throughout thepresent disclosure, these descriptions refer to the action and processesof an electronic device, that manipulates and transforms datarepresented as physical (electronic, magnetic, or optical) quantitieswithin some electronic device's storage into other data similarlyrepresented as physical quantities within the storage, or intransmission or display devices. Exemplary of the terms denoting such adescription are, without limitation, the terms “processing,”“computing,” “calculating,” “determining,” “displaying,” and the like.

Turning now to FIG. 4A, in general terms, the fuel processor 102start-up (at 400) involves lighting off oxidizer 114 (at 402), bringingthe oxidizer 114 to operating conditions (at 404), lighting off the ATR110 (at 406), and then bringing the ATR 110 to operating conditions (at408). The oxidizer 114 light off is the state of the oxidizer 114 whenthere is an ongoing catalysed reaction between the fuel and air in adesired temperature range. Similarly, the ATR 110 light off is the stateof the ATR 110 when it is considered to have an ongoing catalysedreaction between the components of the process feed stream 120 receivedfrom the oxidizer 114. FIG. 4B illustrates (at 410) the oxidizer 114light off more particularly. FIG. 4C illustrates (at 420) the ATR 110light off more particularly.

Referring now to FIG. 4B, the oxidizer 114 light off begins by purging(at 412) the reactor 224 (shown in FIG. 2A) of the oxidizer 114 with airat an initial temperature. The fuel processor 102, prior to start-up,will be at some ambient temperature, i.e., its temperature will not beactively controlled. This ambient temperature will typically be a “room”temperature, or less than approximately 50° C., but this is notnecessary to the practice of the invention. Thus, the “initial”temperature of the purge will usually be the ambient temperature of thefuel processor 102's environment, which will typically by a “room”temperature of less than approximately 50° C.

In the illustrated embodiment, the reactor 224 is purged (at 412) withair 118 supplied from the air subsystem 126 at a rate of 200 L/min for aminimum of 15 minutes, or at least three reactor volumes of air 118. Asthose in the art having the benefit of this disclosure will appreciate,this rate and duration are a function of the volume of the reactor 224.Accordingly, the rate and duration are implementation specific, andother rates and durations may be applied in alternative embodiments. Thecontent of the reactor 224 at this point is 100% air for the illustratedembodiment. However, this is not necessary to the practice of theinvention. The objective is to purge the reactor 224 to just below thelower explosive limit (“LEL”) of the fuel 112 that is to be subsequentlyintroduced. Other air flow rates, durations, and volumes therefore maybe used in alternative embodiments.

The oxidizer light off proceeds by generating (at 414) an ignition heatin at least a portion of the purged oxidizer reactor 224. The manner inwhich the ignition heat is generated will be implementation specific,e.g., by heating at least a portion of a catalyst bed to at least alight off temperature or actuating a spark source. In the illustratedembodiment, the ignition heat is generated in the catalyst bed 257(shown in FIG. 2A) by heating it to at least approximately 280° C. withthe heat exchanger 256. Note that only a portion of the catalyst bed 257needs to be heated in this manner.

Still referring to FIG. 4B, the oxidizer light off next introduces (at416) a fuel to the heated region of the oxidizer reactor 224. Theresulting mixture of the fuel and the air remains below the lowerexplosive limit of the fuel. As those in the art having the benefit ofthis disclosure will appreciate, the lower explosive limit will varydepending on the fuel, and the amount of fuel introduced (at 416) willconsequently depend on the fuel. In the illustrated embodiment, the fuelintroduced is the fuel that will eventually be reformed, i.e., the fuel.As previously mentioned, the fuel 112 is, in the illustrated embodiment,natural gas, although other hydrocarbons may be used. The illustratedembodiment therefore introduces natural gas to achieve an air andnatural gas mixture comprising less than 3.4% natural gas, or an O/C(NG)ratio of greater than 6.0. This is below the LEL of 4.0% natural gas inair, or 5.05 O/C(NG).

The oxidizer light off proceeds by heating (at 418) the oxidizer reactorcontaining the fuel/air mixture to an operating temperature. An“operating temperature” is a temperature high enough to start andsustain a catalyst reaction of the fuel/air mixture with, e.g., thecatalyst bed 257 (shown in FIG. 2). In the illustrated embodiment,oxidizer reactor 224 is heated to a temperature between approximately400° C. and approximately 800° C. At this point, the oxidizer 114 islighted off.

Turning now to FIG. 4C, the ATR 110 light off begins by purging (at 424)the reactor 250 b (shown in FIG. 2B) of the ATR 110 with a fuel at aninitial temperature to at least the upper explosive limit (“UEL”) of thefuel. As with the purge (at 412, in FIG. 4B) of the oxidizer 114, the“initial” temperature of the purge will usually be the ambienttemperature of the fuel processor 102's environment, which willtypically by a “room” temperature of less than approximately 50° C. Thepurge fuel in the illustrated embodiment is the fuel 112 delivered fromthe fuel subsystem 122. As previously noted, the fuel 112 in the presentinvention is natural gas, although other hydrocarbons may be used. TheUEL of the fuel 112 will vary depending on the implementation of thefuel 112. In the illustrated embodiment, this is done by introducing atleast four reactor volumes of the fuel 112 through the reactor 250 b.However, this is not necessary to the practice of the invention so longas the reactor 250 b is purged to at least above the UEL of the fuel112.

The light off of the ATR 110 continues by (at 424), maintaining thenon-pyrophoric shift catalyst (not shown) of the autothermal reformer110 shift 250 d at a temperature sufficient to prevent condensation ofwater therein. In the illustrated embodiment, the ATR 110 employsheaters (i.e., the heat exchanger 290, in FIG. 2B) and cooling coils(i.e., the cooling coil 292, in FIG. 2B) to maintain the temperature ofthe non-pyrophoric shift catalyst between approximately 150° C. and 200°C. The upper bound is placed on the temperature of the non-pyrophoricshift catalyst to prevent damage thereto. Note that, as was statedearlier, the start-up begins with the ATR 110, including the shift 250d, at an ambient temperature. It will therefore be likely that thenon-pyrophoric shift catalyst will first need to be heated. This heatingmay be performed before, during, or after the purge of the reactor 250b, depending on the particular embodiment.

Still referring to FIG. 4C, the ATR 110 light off continues by (at 426)heating the purged reactor 250 b to the light off temperature of thenon-pyrophoric shift catalyst while continuing to flow the fuel 112therethrough. As those in the art having the benefit of the presentdisclosure will appreciate, the light off temperature will varydepending on the implementation of the non-pyrophoric shift catalyst.The illustrated embodiment employs the SELECTRA SHIFT™ as discussedabove and heats the reactor 250 b to approximately 300° C.

The ATR 110 light off then introducing air 118 (at 428) to the reactor250 b to produce an air and fuel mixture (not shown) exceeding the upperexplosive limit (“UEL”) of the fuel 112. The illustrated embodimentimplements the fuel 112 with natural gas, which has a UEL of 17.0% inair, or 1.03 O/C(NG). Thus, the illustrated embodiment introduces air toachieve a concentration of 26% natural gas in air, or an O/C(NG) ratioof 0.6.

The ATR 110 light off concludes by heating (at 430) the reactor 250 b toan operating temperature. In the illustrated embodiment, the operatingtemperature will be between approximately 600° C. and approximately 900°C., and preferably approximately 700° C. The non-pyrophoric shiftcatalyst will be maintained at a temperature of approximately 250° C.More detail on the normal operation of the ATR 110 after start-up isprovided immediately below.

In normal operation, the processor reactor (not shown) of the ATR 104reforms the process feed stream 120 into the hydrogen, orhydrogen-enriched, gas stream and effluent byproducts, such as water.The process feed stream 120 in the illustrated embodiment conveys afuel, air, and water mixture from the oxidizer 114, shown in FIG. 1.FIG. 5 depicts a general process flow diagram illustrating the processsteps included in the illustrative embodiments of the present invention.The following description associated with FIG. 5 is adapted from U.S.patent application Ser. No. 10/006,963, entitled “Compact Fuel Processorfor Producing a Hydrogen Rich Gas,” filed Dec. 5, 2001, in the name ofthe inventors Curtis L. Krause, et al., and published Jul. 18, 2002,(Publication No. US2002/0094310 A1).

The fuel processor 102 process feed stream 120 includes a hydrocarbonfuel, oxygen, and water mixture, as was described above. The oxygen canbe in the form of air, enriched air, or substantially pure oxygen. Thewater can be introduced as a liquid or vapor. The compositionpercentages of the feed components are determined by the desiredoperating conditions, as discussed below. The fuel processor effluentstream from of the present invention includes hydrogen and carbondioxide and can also include some water, unconverted hydrocarbons,carbon monoxide, impurities (e.g., hydrogen sulfide and ammonia) andinert components (e.g., nitrogen and argon, especially if air was acomponent of the feed stream).

Process step A is an autothermal reforming process in which, in oneparticular embodiment, two reactions, a partial oxidation (formula I,below) and an optional steam reforming (formula II, below), areperformed to convert the feed stream 120 into a synthesis gas containinghydrogen and carbon monoxide. Formulas I and II are exemplary reactionformulas wherein methane is considered as the hydrocarbon:CH₄+½O₂→2H₂+CO   (I)The process feed stream 120 is received by the processor reactor fromthe oxidizer 114, shown in FIG. 1. A higher concentration of oxygen inthe process feed stream 120 favors partial oxidation whereas a higherconcentration of water vapor favors steam reforming. The ratios ofoxygen to hydrocarbon and water to hydrocarbon are thereforecharacterizing parameters that affect the operating temperature andhydrogen yield.

The operating temperature of the autothermal reforming step A can rangefrom about 550° C. to about 900° C., depending on the feed conditionsand the catalyst. The ratios, temperatures, and feed conditions are allexamples of parameters controlled by the control system of the presentinvention. The illustrated embodiment uses a catalyst bed of a partialoxidation catalyst in the reformer with or without a steam reformingcatalyst.

Process step B is a cooling step for cooling the synthesis gas streamfrom process step A to a temperature of from about 200° C. to about 600°C., preferably from about 375° C. to about 425° C., to prepare thetemperature of the synthesis gas effluent for the process step C(discussed below). This cooling may be achieved with heat sinks, heatpipes or heat exchangers depending upon the design specifications andthe need to recover/recycle the heat content of the gas stream using anysuitable type of coolant. For instance, the coolant for process step Bmay be the coolant 113 of the thermal subsystem 128.

Process step C is a purifying step and employs zinc oxide (ZnO) as ahydrogen sulfide absorbent. One of the main impurities of thehydrocarbon stream is sulfur, which is converted by the autothermalreforming step A to hydrogen sulfide. The processing core used inprocess step C preferably includes zinc oxide and/or other materialcapable of absorbing and converting hydrogen sulfide, and may include asupport (e.g., monolith, extrudate, pellet, etc.). Desulfurization isaccomplished by converting the hydrogen sulfide to water in accordancewith the following reaction formula III:H₂S+ZnO→H₂O+ZnS   (III)The reaction is preferably carried out at a temperature of from about300° C. to about 500° C., and more preferably from about 375° C. toabout 425° C.

Still referring to FIG. 5, the effluent stream may then be sent to amixing step D in which water 116 received from the water subsystem 124,both shown in FIG. 1, is optionally added to the gas stream. Theaddition of water lowers the temperature of the reactant stream as itvaporizes and supplies more water for the water gas shift reaction ofprocess step E (discussed below). The water vapor and other effluentstream components are mixed by being passed through a processing core ofinert materials such as ceramic beads or other similar materials thateffectively mix and/or assist in the vaporization of the water.Alternatively, any additional water can be introduced with feed, and themixing step can be repositioned to provide better mixing of the oxidantgas in the CO oxidation step G (discussed below). This temperature isalso controlled by the control system of the present invention.

Process step E is a water gas shift reaction that converts carbonmonoxide to carbon dioxide in accordance with formula IV:H₂O+CO→H₂+CO₂   (IV)The concentration of carbon monoxide should preferably be lowered to alevel that can be tolerated by fuel cells, typically below 50 ppm.Generally, the water gas shift reaction can take place at temperaturesof from 150° C. to 600° C. depending on the catalyst used. Under suchconditions, most of the carbon monoxide in the gas stream is convertedin this step. This temperature and concentration are more parameterscontrolled by the control system of the present invention.

Returning again to FIG. 5, process step F is a cooling step. Processstep F reduces the temperature of the gas stream to produce an effluenthaving a temperature preferably in the range of from about 90° C. toabout 150° C. Oxygen from an air subsystem (not shown) is also added tothe process in step F. The oxygen is consumed by the reactions ofprocess step G described below.

Process step G is an oxidation step wherein almost all of the remainingcarbon monoxide in the effluent stream is converted to carbon dioxide.The processing is carried out in the presence of a catalyst for theoxidation of carbon monoxide. Two reactions occur in process step G: thedesired oxidation of carbon monoxide (formula V) and the undesiredoxidation of hydrogen (formula VI) as follows:CO+½O₂→CO₂   (V)H₂+½O₂→H₂O   (VI)

The preferential oxidation of carbon monoxide is favored by lowtemperatures. Since both reactions produce heat it may be advantageousto optionally include a cooling element such as a cooling coil, disposedwithin the process. The operating temperature of process is preferablykept in the range of from about 90° C. to about 150° C. Process step Greduces the carbon monoxide level to preferably less than 50 ppm, whichis a suitable level for use in fuel cells.

The reformate 105 exiting the fuel processor is a hydrogen rich gascontaining carbon dioxide and other constituents which may be presentsuch as water, inert components (e.g., nitrogen, argon), residualhydrocarbon, etc. Product gas may be used as the feed for a fuel cell orfor other applications where a hydrogen rich feed stream is desired.Optionally, product gas may be sent on to further processing, forexample, to remove the carbon dioxide, water or other components. Table1 presents additional information on the normal operation of the ATR110. TABLE 1 Non-Pyrophoric Shift Catalyst Areas of Operation Reducing(Reformate) Oxidizing (Air) Maximum Temperature when No steam duringoxidizing operating <300° C. Up to 350° C. for transients <30 H2O isreversible; 220° C. minutes overnight; 400° C. in 1 hour If overtemperature, non-reversible, methenation begins No liquid water Noliquid water.

Eventually, the operational cycle ends, and the fuel processor 102 isshutdown, as shown in FIG. 6A (at 600). The shutdown may be planned, asin the case for maintenance, or unplanned, as when a shutdown errorcondition occurs. The oxidizer 110 and ATR 110 reactors 256 and 250 b,respectively, are, in general terms, purged and cooled. On transition tothe shutdown state, the air subsystem 126, the water subsystem 124, andthe thermal subsystem 128 are providing air 118, water 116, and thermalcontrol to the oxidizer 110 and the ATR 110. In the illustratedembodiment, the ATR 110 is first purged (at 602) and shutdown (at 604),followed by the oxidizer 110 purge (at 606) and shutdown (at 608).

Turning now to FIG. 6B, to shutdown and purge the ATR 110, the airsubsystem 126 terminates the flow of air 118 (at 610), followed by thewater subsystem 124 terminating (at 612) the flow of water 116 to thereactor 250 b of the ATR 110. The fuel subsystem 122 then continues (notshown) the flow of fuel 112 as the reactor 250 b of the ATR 110 purges(at 614) with the fuel 112. The components are allowed to cool to ashutdown temperature (at 616). The shutdown temperature may be anambient temperature. In the illustrated embodiment, however, the thermalsubsystem 128 continues to cool (not shown) various components of theATR 110, including the reactor 250 b until they cool to belowapproximately 50° C., whereupon the cooling coils are turned off.

To shutdown and purge the oxidizer 110, as is shown in FIG. 6C, the fuelsubsystem 122 terminates (at 618) the flow of fuel 112 to the reactor224 of the oxidizer 110, whereupon the oxidizer reactor 224 is purged(at 620) with air 118 from the air subsystem 126. The oxidizer reactor224 is purged until it reaches a predetermined, shutdown temperature, asopposed to the ATR reactor 250 b, which is purged by volume. Thisapproach is taken in the oxidizer reactor 224 purging becausedifferences in catalyst loading in different parts of the bed may bemore active than the other. In the illustrated embodiment, the oxidizerreactor 224 is purged to an ambient, or “room,” temperature, or atemperature below approximately 50° C. Once the oxidizer reactor 224 ispurged, the air subsystem 126 terminates (at 622) the air supply to theoxidizer 110 and shuts down the components (e.g., the compressor) of theair subsystem 126. The water subsystem 124, fuel subsystem 122, andthermal subsystem 128 also shut down the components of the watersubsystem 124, fuel subsystem 122, and thermal subsystem 128.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the invention.Accordingly, the protection sought herein is as set forth in the claimsbelow.

1. A method for lighting off an oxidizer in a fuel processor,comprising: purging a reactor of the oxidizer with air at an initialtemperature; generating an ignition heat in at least a portion of thepurged oxidizer reactor; introducing a fuel to the heated region of theoxidizer reactor, the resulting mixture of the fuel and the airremaining below the lower explosive limit of the fuel; and heating theoxidizer reactor containing the fuel/air mixture to an operatingtemperature.
 2. The method of claim 1, wherein purging the oxidizerreactor at the initial temperature includes purging the oxidizer reactorbelow approximately 50° C.
 3. The method of claim 1, wherein purging theoxidizer reactor at the initial temperature includes purging theoxidizer reactor at ambient temperature.
 4. The method of claim 1,wherein purging the oxidizer reactor includes purging the oxidizerreactor through at least thee reactor volumes of air.
 5. The method ofclaim 1, wherein generating the ignition heat includes heating at leasta portion of a catalyst bed to at least a light off temperature.
 6. Themethod of claim 1, wherein generating the ignition heat includesactuating a spark source.
 7. The method of claim 1, wherein generatingthe ignition heat includes generating an ignition heat of approximately280° C.
 8. The method of claim 1, wherein introducing the fuel includesintroducing natural gas.
 9. The method of claim 8, wherein introducingthe natural gas includes introducing the natural gas to achieve an airand natural gas mixture having an O/C(NG) ratio of greater than 6.0. 10.The method of claim 1, wherein heating the oxidizer reactor to anoperating temperature includes heating the oxidizer reactor to atemperature between approximately 400° C. and approximately 800° C. 11.A method for shutting down an autothermal reformer employing anon-pyrophoric shift catalyst in a fuel processor, comprising:terminating air flow to the autothermal reformer reactor; terminatingwater flow to the autothermal reformer reactor after terminating the airflow; purging the autothermal reformer reactor with a fuel; and allowingthe autothermal reformer reactor to cool to a shutdown temperature. 12.The method of claim 11, wherein the shutdown temperature is an ambienttemperature.
 13. The method of claim 11, further comprising activelycooling the autothermal reformer reactor to less than approximately 50°C.
 14. The method of claim 11, wherein purging the autothermal reformerreactor with the fuel includes purging the autothermal reformer reactorwith natural gas.
 15. A method for shutting down an oxidizer for usewith an autothermal reformer employing a non-pyrophoric shift catalyst,comprising: terminating the flow of the fuel to a reactor of theoxidizer; purging the oxidizer reactor with air until the temperaturewithin the oxidizer reactor reaches a shutdown temperature; andterminating the air flow to the purged oxidizer reactor.
 16. The methodof claim 15, wherein the shutdown temperature is an ambient temperature.